The invention relates to a transfer film, in particular hot-stamping film, the use of a transfer film, a film, a security document, and a method for producing a transfer film.
Security documents such as for example banknotes, passports, ID cards, check cards, credit cards, visas or certificates are often provided with security elements to increase protection against forgery. Such security elements are used to check security documents for authenticity and allow forgeries or manipulations to be recognized. Furthermore, security elements on security documents increase protection against illegal duplication. Such security elements are moreover used in the field of commercial products or product packaging, the authenticity of which is to be verified.
Security elements often have light-bending, diffractive structures such as for example holograms which, after application to a security document, are intended to increase its protection against forgery. These security elements offer the observer striking optically variable effects. In addition to the already-mentioned security elements which are based on optically diffractive effects, optically variable thin-film-layer elements are often used, which give an observer a different color impression for example, at different observation angles. Such thin-film-layer elements are based on interference effects.
Security elements with, for example, diffractive structures are often transferred onto the security documents to be protected by means of transfer methods. For this, a transfer layer is transferred, for example under the action of heat and pressure, from a carrier film onto a target substrate to which the transfer layer adheres, using an adhesive layer.
In contrast, further security features which also increase the protection of the security documents against forgery, such as for example optically variable effect colors or soluble dyes, are printed directly onto the target substrate. For this, the screen printing method is usually used, in which in particular the achievable brilliance and the distinctiveness of the color effects depend on the nature of the target substrate. The target substrate can be in the form of sheets or as a roll.